Pond Scum Prized Again
as Potential Biofuel

By Carl Zimmer

The four flasks look like they’re
filled with bubbling lime juice. “If you look closely,” says Hamid
Rismani-Yazdi, a Yale postdoctoral researcher, “you can see the algae.” It’s
true: put your nose to the Pyrex, and you can make out tiny flecks of Dunaliella
tertiolecta, an ocean-dwelling species, riding the turbulence.

Rismani-Yazdi’s flasks may look
like nothing more than improvised aquariums. But Rismani-Yazdi and his
colleagues have great hopes for the algae they’re rearing. It’s possible that
these organisms may help start an industrial revolution.

Like a growing number of other
scientists, they think algae may someday be able to churn out huge amounts of
environmentally friendly fuel. It’s an idea on which investors are also
betting, and in a big way. Some $800 million in venture capital has flowed into
companies working on algae fuels, most of it arriving over just the past few
months. From green flasks like these may come a postpetroleum economy.

At least that’s the idea. Despite
all the cash and all the headlines, the quest for algae biofuel has a long way
to go. There are many open questions about whether it can really work on an
industrial scale. Last year three professors at Yale—Jordan Peccia, Julie
Zimmerman and Paul Anastas—decided to combine the brainpower in their labs to
solve many of the mysteries about algae fuel. They are deciphering the complex
network of genes inside of algae to learn how to manipulate them to be better
fuel factories. And they are also deciphering the complex economic network that
will emerge to support the industrial-scale production of fuel from algae.
After all is said and done, they want to know if we would actually be better
off environmentally if algae, like the ones in Rismani-Yazdi’s flasks, fueled
our cars and airplanes.

“You can grow algae everywhere, so you can make them where people are using them.”

Julie Zimmerman

Today the algae have decided to be
particularly mysterious. Rismani-Yazdi, who works in Peccia’s lab, has been
adjusting his recipe of artificial seawater to coax his Dunaliella tertiolecta into growing quickly. The algae have become dense
enough to give his flasks a lime-green hue. But Rismani-Yazdi would like them
to grow a thousand times denser. To show what he’s shooting for, he picks up
another flask, which looks as if it’s full of spinach soup. It’s crammed with a
freshwater species called Scenedesmus dimorphus.

“Something is limiting their
growth,” he says, looking back to the lime-green flasks of Dunaliella
teriolecta. Maybe his fluorescent lamps are
too bright. Maybe he’s giving them too much carbon dioxide. Or maybe it’s
something he hasn’t thought of yet.

Peccia listens to Rismani-Yazdi
describe his frustration. He shrugs his shoulders with a faint smile. It’s a
puzzle that he’s very familiar with. “One alga looks just like another, but
they respond so differently,” says Peccia, associate professor of chemical
engineering. “Sometimes they don’t want so much light; sometimes they don’t
like the nitrogen. After a while, we talk about them like people.”

The current excitement over algae
may be new, but the basic concept underlying it is old. Today we produce fossil
fuels, like gasoline and diesel, from crude oil buried deep in the ground. That
crude oil got its start as carbon compounds in organisms that lived millions of
years ago. Scientists have long wondered whether it would be possible to skip
those millions of years of waiting—not to mention the drilling and the other
demands of petroleum production—and gather energy-rich compounds from living
things.

Some of the most promising
compounds are oily molecules called lipids. All living things make them. Our
bodies make lipids to build the membranes of our cells and to store extra
energy for lean times. In the past, people have extracted lipids from animals
for fuel. Lipid-rich whale oil fueled lamps and lighthouses across the United
States during the 19th century,
for example.

You can’t fuel a modern economy on
whale oil, though. Whales are just too scarce and reproduce themselves too
slowly. As a result, whalers nearly drove many species of whales extinct by the
early 20th century. But there are other organisms that make lipids in far
greater quantities and at a far-faster rate. They are algae.

Algae is a broad term that refers to most of the organisms that live in
water and capture energy from the sun. One kind, called cyanobacteria, is also
known as blue-green algae for its color. Like other bacteria, cyanobacteria are
very small, have few genes and normally make a small supply of lipids. Other
kinds of algae, often called microalgae, have cells much more like ours.
(That’s because they’re more closely related to us than to bacteria.) The cells
of these microalgae are big and complex. In many cases, they also have many
times more genes than cyanobacteria. And—most importantly for the search for
new kinds of fuel—they produce a remarkable quantity of lipids. In some species
of microalgae, lipids can take up over half the mass of a cell.

Thirty years ago, the U.S.
Department of Energy launched the Aquatic Species Program to investigate the
possibility of getting fuel from microalgae. It might be possible, scientists
reasoned, to grow algae, extract lipids from them and transform those lipids into diesel or other kinds of fuel.
Fanning out across North America, they gathered 3,000 promising, lipid-rich
strains. They tested the algae in massive racetrack-shaped tanks. They
engineered algae with genes to make them churn out extra lipids. And they
explored different kinds of chemical reactions that could pull those lipids out
of the algae.

Over its 17-year lifetime, the
Aquatic Species Program made a lot of important discoveries about the basic
biology of algae. But despite these achievements, the program’s scientists
never got the cost of algae-derived fuel down low enough to make it a practical
alternative to fossil fuels. In 1996, the Department of Energy closed the
program down in a wave of budget cuts.

Thirteen years later, however, the
algae are back. “The landscape has changed,” says Zimmerman, assistant
professor of green engineering at F&ES.

Many experts are now warning
that the world’s oil supply cannot
expand fast enough to satisfy the growing demand for energy. As a result, they
warn, we can expect more price spikes like the ones that have shocked the
economy in recent years. At the same time, petroleum’s toll on the environment
is becoming clearer, especially its huge role in warming the Earth’s climate.

Concerns like these have led the
U.S. government and the energy industry to get serious about all kinds of
alternative fuels. And that includes biofuels—the fuels derived from living
things. Today ethanol from corn and diesel from other crops, such as soybeans,
make up the majority of biofuels on the market. These biofuels emit carbon
dioxide just like petroleum when they power a car, but they have, at least in
theory, a big advantage over fossil fuels. In order for biofuels to be made in
the first place, plants have to suck carbon dioxide out of the air. The gas
they draw down could potentially balance the climate books.

Unfortunately, many experts now
argue, biofuels from crops have hidden costs. “When you count all the
pesticides and fertilizer and farming and the water that goes into it, it isn’t
really a good environmental strategy,” says Zimmerman.

It’s also a strategy that can force
us to choose between food and fuel. That’s because it takes a lot of land to
grow corn and soybeans for biofuel, land that could otherwise be dedicated to
feeding people. In 2006, University of Minnesota biologist David Tilman and his
colleagues reported that dedicating all of the current U.S. corn crop to
ethanol would satisfy just 12 percent of the country’s demand for gasoline. If
all the soybean farms shipped their beans to refineries, they would satisfy
only 6 percent of the country’s demand for diesel fuel.

Outside the United States, biofuels
are having even more devastating impacts. The demand for palm oil for biofuel
has spurred corporations to clear millions of acres of tropical forests for
plantations. Conservation biologists have warned that the rapid destruction of
these forests will threaten many species of plants and animals. Oil palm
plantations may drive many populations of orangutans extinct within 10 years,
for example.

These drawbacks to crop biofuels
have led a number of researchers to take another look at algae. On paper, at
least, algae don’t carry the risks of crop biofuels. They may be a much more
efficient source of lipids, for example. “In soybeans, it’s just in the beans,”
says Peccia. “In algae, it’s the whole thing.”

Unlike soybeans, Peccia points out,
algae don’t need soil. “They can just live on wastewater.” Engineers would have
a lot of options about where to put their algae tanks. Some species would
thrive in the sunny deserts of the Southwest, while others would do well in the
cloudy Northeast. It might even be possible to grow marine algae in the ocean,
in much the same way that fish are farmed. “You can grow algae everywhere, so
you can make them where people are using them,” says Zimmerman.

One of the reasons that crop
biofuels aren’t as green as they may seem is that they require lots of
fertilizers, which then get carried into rivers and oceans, where they foster
the growth of oxygen-devouring bacteria, creating so-called dead zones where
few animals can survive. Algae, on the other hand, can be fertilized with
materials that can then be captured as they leave a tank. And algae can also be
fertilized in ways that crops cannot. The carbon dioxide belched out of a
coal-fired power plant, for example, can get piped into an algae tank,
stimulating growth.

Few people outside of the
alternative-energy world knew about algae’s renaissance until last July. Exxon
announced that it was plowing $600 million into algae research. The oil giant
entered into a partnership with Synthetic Genomics, headed by Craig Venter, who
pioneered sequencing the human genome in the 1990s. Over the past few years,
Venter and his colleagues have been inserting genes into cyanobacteria to
increase their production of lipids. Exxon expects to have small-scale plants
in operation in five to 10 years.

The Wall Street Journal reacted to the news by declaring that the world had
entered “the summer of algae.” Other companies were getting into the algae game
as well. Solazyme, a corporation based in San Francisco, announced in June that
its funding had reached $76 million. In September it announced that the
Department of Defense had picked Solazyme to supply 20,000 gallons of fuel for
Navy jets. Another company, Sapphire Energy, has $100 million in funding and
promises that by 2011 it will be producing 1 million gallons of diesel and jet
fuel from algae.

Yet these promises do not, in
themselves, guarantee that algae fuel will actu-ally make financial sense.
According to one estimate, it’s still 20 times more expensive to make than
crude oil. And some skeptics don’t believe that the recent flurry of investment
reflects any profound advances in dealing with the great problems associated
with fuel derived from algae.

The best way to get a lot of lipids
out of algae, for example, is to put them under stress. If Scenedesmus
dimorphus is fertilized with a lot of
nitrogen, for example, its cells will end up 20 percent lipids. On a
low-nitrogen diet, that figure rises to 35 percent. Algae probably evolved this
strategy as a way to survive temporary famines. In other words, it’s not
something they can do indefinitely. If you stress algae for too long, says
Peccia, “they’ll just give out.”

In 2008, Peccia, Zimmerman and
Anastas decided to get into the algae fuel game. While corporations were just
tweaking the algae and observing how many lipids they could get out, the Yale
researchers chose a different strategy. “It’s a different way of going about
things,” says Anastas, Teresa and H. John Heinz III Professor in the Practice
of Chemistry for the Environment.

Peccia has been leading the team’s
effort to get to know algae in their most intimate details. “We just want to
understand how they operate, really in the most fundamental way,” says Peccia.
For all the research that has gone into algae, for example, scientists still
know nearly nothing about the genes they use to make lipids. No one has even
sequenced the genomes of any of the lipid-rich microalgae. “We don’t really
know how it all works,” says Peccia.

Because the genomes of microalgae
are so big, Peccia and his colleagues have decided not to sequence all of their
DNA. Instead, they’re just searching for the genes they use to make extra
lipids. To find them, the scientists raise algae in different conditions. For instance,
they rear some of their algae with a lot of nitrogen and some of them with
barely any. The algae respond to these different conditions by switching on
different genes. Peccia and his colleagues then rip open the algae. They fish
out copies of the active genes, called messenger RNAs. From those molecules,
the scientists can determine the sequence of the genes and start to gather
clues about their function.

Peccia and his colleagues are now
mapping out the gene networks that algae use to ramp up their lipid production.
They hope that this knowledge will allow them to precisely manipulate algae
into making more lipids with few side effects. It will then be possible to
abandon the current brute-force methods of starvation.

Even if Peccia and his colleagues
can manipulate algae to become champion lipid makers, however, they will still
face some serious challenges in getting the organisms to thrive outside of a
laboratory flask. The Earth’s waters are loaded with algae, and their diversity
is so vast that scientists are only just starting to catalog it. Some of those
species will inevitably slip into the tanks where engineers rear their designer
algae. “They’re going to have to learn how to compete with these constant
insults of micro-algae coming in,” says Peccia. If they don’t, they’ll get
outcompeted and the tank will become overwhelmed by the wrong kinds of algae.

Peccia has been probing the biology
of algae to look for ways that he can help them win in the real world. He and
his colleagues have found that Scenedesmus dimorphus grows nicely when levels of carbon dioxide are high.
In fact, they keep growing when other species of algae die from carbon dioxide
poisoning. By pumping extra carbon dioxide into algae tanks, engineers may be
able to keep the right species thriving. “If we don’t bubble high CO2 in, the
natural algae outcompete it,” says Peccia.

The challenges don’t stop there,
however. Once scientists can successfully rear their algae outside of the lab,
they’ll then have to extract lipids from them. Right now, the only practical
method involves pumping chlorinated compounds similar to PCBs and dioxin into
the algae. “It’s not very efficient, and it’s not very green,” says Zimmerman.
In fact, it’s poisonous. Chlorinated compounds can pollute soil and groundwater
for decades.

Zimmerman is now trying to borrow a
trick from dry cleaners. A lot of the dirt that dry cleaners get out of clothes
is made up of lipids. In the past, they’ve used chlorinated compounds, but
recently they’ve switched over to high-pressure, superheated carbon dioxide. If
you squeeze and heat carbon dioxide enough, it starts to act like chlorin-ated
compounds and can grab certain kinds of lipids. “It’s really nice: you can
recapture the CO2 and reuse it. It’s a much greener way to go,” says Zimmerman.

Anastas is investigating what to do
with another major source of waste: the algae. Once lipids for fuel are
extracted from algae, there’s still a lot of biomass left over. Anastas is
approaching the problem of this waste the way oil companies do when they refine
petroleum. They don’t simply throw out what’s left over when they’ve produced
gasoline. “Every little bit of that black stuff coming out of the ground is
finding some kind of purpose,” says Anastas.

Just as petroleum can be turned
into everything from plastic to asphalt, Anastas wants to develop new products
using what’s left over from the production of fuel from algae. It’s a fertile
field for invention, he says, because the molecules in algae are more intricate
than the simple straight chains of hydrogen and carbon that come out of
petroleum. “You can take advantage of their complexity to make new molecules,”
he says.

By developing new products (such as
fire-retardant building materials, for example), Anastas hopes to both reduce
the environmental impact of algae and boost their value. “Green is the color of
the environment, and it’s also the color of money,” he says. “Taking things out
of the waste stream changes the economic equation.”

The Yale researchers are spending a
lot of their time investigating particular steps in the process of turning
algae into fuel. But they also want to see how the whole system will work in
advance. This may sound like clairvoyance, but engineers have a fairly
well-developed method for modeling complicated industrial processes. Zimmerman
herself has made these models for Ford to help them plan out new systems for
manufacturing lubricants for their cars. Now she’s building a model of the
entire process of getting fuel from algae. “We’re looking at it from the cradle
to the end of life,” she says.

The model is still in its early
stages, but Zimmerman can already see that algae do indeed promise to have much
less impact on the environment than crop biofuels. She is also using the models
to evaluate which methods for growing algae are the greenest. It appears, for
example, that conventional racetrack-shaped tanks are not the best design. Her
model points instead to designs in which water flows through spiraling tubes,
allowing more sunlight to penetrate the water and spur the algae to grow.

Zimmerman’s model may also help
engineers cope with the complexities of the energy economy. As the market
changes, the profits from algae fuel may change in mysterious ways. Zimmerman
wants to use her model to determine how much fuel or how many other products
should be generated from algae to make the entire process as valuable as
possible.

That’s a lot of complexity to add
to a project that’s already enormously ambitious. But if Zimmerman and her
colleagues can figure out how to make millions of gallons of green fuel from
the algae living in their lab, it will be well worth the extra effort.

“You feel like, if you could figure it out, it would make a
huge difference,” she says.